Vision Science Quiz

Dark Adaptation and Absolute Threshold in Vision

• The dark adaptation process involves two distinct parts, representing cone and rod function.
• Cones recover sensitivity first, followed by rods after about 8-10 minutes, with peak rod sensitivity occurring after 30-35 minutes in the dark.
• As cones recover sensitivity first, the target stimulus appears violet; as rod sensitivity improves, the stimulus becomes colorless.
• The dark adaptation curve varies depending on the individual's thresholds and the eccentricity in the visual field.
• In clinical applications, knowledge of dark adaptation function can help diagnose and treat patients with night blindness and hereditary vision disorders.
• The absolute threshold of scotopic vision is the lowest light energy level of a stimulus that can be perceived.
• Cone density is highest centrally and reduces into the periphery, while rod density peaks at about 20° in the periphery.
• The observer was dark adapted for 30-40 minutes and fixated on a small red spot while a stimulus was presented at 20° in the temporal retinal periphery to measure the absolute threshold.
• The energy from the light source at the plane of the eye was 2.1 x 10^17 to 5.7 x 10^17 joules, with 5-14 quanta absorbed by the rod photopigments at absolute threshold.
• A single quantum is sufficient to activate a rod, but a single activated rod is not sufficient for seeing due to the pooling of rod signals onto ganglion cells, which allows for high sensitivity but poor spatial resolution.
• The combination of signals from multiple rods onto a ganglion cell is called 'pooling', enabling the scotopic rod system to have high sensitivity to detect light but lesser ability to discern individual lights.
• The study aimed to measure the absolute threshold and understand the minimum number of neural impulses required for vision, shedding light on the functioning of the eye in low-light conditions.